Abstract [en]

Cyanobacteria are unique eubacteria with an organized subcellular compartmentalization of highly differentiated internal thylakoid membranes (TM), in addition to the outer and plasma membranes (PM). This leads to a complicated system for transport and sorting of proteins into the different membranes and compartments. By shotgun and gel-based proteomics of plasma and thylakoid membranes from the cyanobacterium Synechocystis sp. PCC 6803, a large number of membrane proteins were identified. Proteins localized uniquely in each membrane were used as a platform describing a model for cellular membrane organization and protein intermembrane sorting and were analyzed by multivariate sequence analyses to trace potential differences in sequence properties important for insertion and sorting to the correct membrane. Sequence traits in the C-terminal region, but not in the N-terminal nor in any individual transmembrane segments, were discriminatory between the TM and PM classes. The results are consistent with a contact zone between plasma and thylakoid membranes, which may contain short-lived "hemifusion" protein traffic connection assemblies. Insertion of both integral and peripheral membrane proteins is suggested to occur through common translocons in these subdomains, followed by a potential translation arrest and structure-based sorting into the correct membrane compartment.

Pisareva, Tatiana

Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.

2009 (English)Doctoral thesis, comprehensive summary (Other academic)

Abstract [en]

Cyanobacteria constitute a unique group of eubacteria, possessing outer and plasma membranes as well as internal thylakoid membranes, the site for both photosynthesis and respiration. The combination of sucrose density centrifugation and two-phase partitioning methods leads to purification of different membranes from the cyanobacterium Synechocystis sp. PCC 6803 (referred to as Synechocystis). The standard proteomics methods, based on 1D- and 2D-gel electrophoresis, followed by protein digestion and MALDI-TOF MS, led to identification of 76 thylakoid and 51 plasma membrane proteins. In order to increase the number of identified proteins a shotgun proteomics approach was employed. Proteins were digested in complex mixtures, followed by LC separation of obtained peptides coupled to MS/MS. This approach led to identification of 379 different thylakoid and plasma membrane proteins, of which 124 were integral membrane proteins.

The complex membrane organization of Synechocystis requires a unique system for transport and sorting of proteins into extracytosolic cell compartments. Obtained gel-based and shotgun proteomics data as well as results of the multivariate sequence analysis of both soluble and integral membrane proteins allowed to suggest a new mechanism for membrane organization and protein sorting in Synechocystis. The plasma and thylakoid membranes are proposed to be dynamically connected and both soluble and integral membrane proteins are inserted into connection points.

The Synechocystis genome possesses two genes encoding leader peptidases. Proteomic studies revealed that Sll0716 is localized in the thylakoid membrane (LepT), whereas Slr1377 in the plasma membrane (LepP). The BN/SDS-PAGE of the total membranes from mutant LepT revealed that LepT is directly involved in the processing of several photosynthetic and lumenal subunits, required for the assembly and function of PSI and maintaining of the thylakoid membrane organization in Synechocystis.

Research subject

Identifiers

Public defence

Opponent

Robinson, Colin

Department of Biological Sciences, University of Warwick, UK.

Supervisors

Norling, Birgitta

Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.

Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: In progress. Paper 5: In progress.
Available from: 2009-09-08 Created: 2009-08-07 Last updated: 2011-05-03Bibliographically approved